1. Field of the Invention
The present invention relates to gas or liquid seals and, more particularly, to brush seals for sealing high pressure areas from low pressure areas.
2. Description of the Related Art
Over the last decade, brush seals have emerged to be a very promising technology for sealing high pressure areas from low pressure areas such as those found in gas turbine engines. Indeed, there is a substantial reduction, e.g., an order of magnitude, in brush seal leakage flow over the present day technology of labyrinth seals, the main disadvantage associated with labyrinth seals being that the clearance of the seal around the shaft tends to increase appreciably over time due to shaft excursions and thermal growth. The resulting increase in parasitic leakage can cause as much as 17 percent loss in power and 7.5 percent increase in specific fuel consumption in the case of engines.
One drawback of current brush seal designs is that the minimum clearance between the backplate and the shaft must be at least great enough to accommodate various transients that the seal is expected to experience. Some of the transients include thermal growth of the shaft, centrifugal growth of the shaft, runout of the shaft, thermal bowing of the shaft on heat-up, shaft movement due to acceleration (turning acceleration), shaft vibration, and eccentricity of the seal housing with respect to the shaft center line.
Seal leakage increases and maximum pressure capability of the seal decreases, however, as the clearance between the shaft and backplate is increased. Thus, seal performance is improved if the seal can be made with a smaller backplate clearance.